The inventive subject matter relates to part ejector mechanisms on lathe machines and in particular part ejector mechanisms on CNC metal lathe machines.
Metal lathes machine metal bar stock. Older metal lathes required manual loading of the bar stock into a headstock having a spindle and collet that securely held and rotated the stock while machine tools would machine the part. A tailstock could also hold and rotate the bar stock. Sometimes longer work pieces would be held by the headstock and the tailstock. The tailstock may hold the bar stock while a finished or partially finished work piece is cut from bar stock. Additionally the tailstock could hold the work piece to allow secondary machining on the work piece from angles that may not be possible when the work piece is held by the headstock.
Many type of machine tools are employed to work the bar stock such as cutters and drills that are mounted on tool holders that are in turn mounted on a bed of the lathe. These older lathes were manually operated and thus were not enclosed because an enclosure would interfere with operator access to the work piece.
CNC (computer numerical controlled) lathes improve on the older lathes by providing significantly greater precision and repeatability. CNC lathes may be programmed manually, or directly from CAD/CAM files. In CNC lathes a main spindle holds the bar stock and machine tools are mounted onto a turret or tool block. The tool block moves along slides so that individual tools may by indexed into position to work on the work piece. Typically, tool blocks may move in multiple directions to control the orientation of the tool to the work piece, that is, for example, the angle, height, and depth of a cut may be controlled simultaneously. When work on the work piece reaches a predetermined point in the process, a sub-spindle engages the work piece and the piece is cut from the bar stock. Further work may then be performed on the work piece while the sub-spindle holds it.
CNC lathes are typically enclosed for safety reasons. Also, CNC lathes may be automated to repeat a process to produce multiple work pieces in succession. These automatic machine processes require a means to eject the work piece from the sub-spindle when work is completed.
Swiss-style CNC lathes further improve on the CNC lathe by employing a guide bushing in front of the main spindle collet. The bar stock extends through the guide bushing, which steadies the bar stock/work piece and the machine tools are deployed to work on the work piece near the guide bushing. The main spindle moves along the axis of rotation (referred to as the Z-axis) and the work piece extends further or lesser through the guide bushing as necessary to position the portion of the work piece currently undergoing machining. This arrangement steadies the work piece and because all the tools work on the work piece near a point of support, greater precision is achieved.
At a predetermined point in the process, the bar stock is moved further through the guide bushing and the work piece is engaged by the sub-spindle and cut from the bar stock. Further machining may occur as the sub-spindle holds the work piece. When all work is complete, the work piece must be ejected so the process may be repeated.
In Swiss-style lathes, the distance from the guide bushing to the sub-spindle is limited thus impeding the ability to design a path for automatically removing finished work pieces that are relatively long. In these cases, the work piece may be ejected out the “back” of the machine, that is, ejected rearwardly out of the sub-spindle in a direction away from the main spindle.
Prior art parts ejectors employ mechanical ejectors where a work piece is pushed out of the sub-spindle by a rod or cable and longer work pieces again poses a problem because it is impractical to employ a push rod long enough to push a long work piece all the way out. As a consequence, prior art ejectors would partially push a work piece out and then load a spacer, or chub, and then load the next work piece. After the subsequent work piece was completed, it would be partially ejected by the mechanical ejector and as it was partially pushed out it would “eject” the prior work piece.